Nearly all motor vehicles today are provided with inflatable restraint systems to protect both the driver and passengers in the event of a collision. The airbag system for the passenger side of the vehicle generally includes an inflator and reaction canister located behind the instrument panel and the airbag inflates through an opening in the panel. That opening may be covered by a rectangular shaped door that is flush mounted in the opening and is moved out of the way on a hinge or tethers by the deploying airbag. In some applications, the door that covers the opening may be “invisible” to the occupants of the vehicle, that is, hidden behind a surface covering of skin and foam which is pre-weakened by a groove formed on the backside of the skin layer to allow a predictable tearing of the skin. A separate door substrate is hinged or tethered to the instrument panel or canister to control door opening.
Vehicles such as small trucks, SUV's and small to medium sized cars often will use a hard panel construction, without a separate soft skin and padded foam layer, to reduce cost. In these cases, a separate airbag door, instrument panel and door chute are assembled over the canister. To control the path of the airbag as it expands, a deployment chute transitions the space between the canister where the bag is stored and the back of the airbag door to assure that the bag does not expand in an undesirable direction. Use of a hard door separate from the remainder of the instrument panel may allow replacement of only the door portion after a low speed deployment, as the remainder of the instrument panel may not be damaged. In still other applications, the hard instrument panel may be of unitary construction with a pre-weakened seam of reduced cross-section formed on the underside of the panel, outlining the periphery of the airbag door. Hinges, tethers, reinforcements and chutes are then post-attached to the molded hard panel.
Additionally, it is known in the art to use both hinges and tethers to control the opening and travel of the door or door substrate. In U.S. Pat. Nos. 5,685,930; 5,564,731; 5,804,121; 5,902,428 and 5,975,563 to Gallagher, et al and commonly assigned to the assignee of the present invention and included herein by reference, a molded motor vehicle instrument panel made of thermoplastic material having an integral airbag deployment door for a passenger side airbag that is defined by a tear seam and normally retained by an integral flexible mounting/hinge flange is disclosed.
In U.S. Pat. Nos. 5,685,930 and 5,902,428 the door is retained by a supplemental tethering hinge which is formed separately from the panel and attached by welding or an adhesive. The supplemental tethering hinge contains a loop or fold 63 as slack to let the door separate and move controllably away from the instrument panel to allow the bag to expand through the opening.
In U.S. Pat. Nos. 5,564,731 and 5,975,563 the flexible tethering hinge is described as being of sheet material, thermosetting, thermoplastic, metal mesh or woven fabric of plastic or natural fibers and attached by mechanical fasteners or hot staked bosses on the inner side of the door portion.
U.S. Pat. Nos. 5,975,563 and 5,804,121 are directed at an integral mounting hinge/flange on which is formed a bonded layer of second plastic material on one side of the flange and on the inner side of a potentially frangible portion of the door. The second plastic material has the physical characteristic of remaining ductile at low temperatures at which the instrument panel plastic material becomes brittle and as a result, the bonded layer forms a tether to retain the door in a controllable manner as it separates from the instrument panel when the airbag is deployed.
In U.S. Pat. No. 5,765,862 to Autoliv ASP, Inc., an inflatable airbag assembly mounted in a rectangular opening in the vehicle instrument panel is disclosed having bracket means, a plurality of thermoplastic resin fasteners and an integrally formed tether support bar 18 for a tether 20 that is connected between the door 14 and a bracket 22, on the airbag module 16.
U.S. Pat. No. 5,533,746 to Morton International recites “a cover for covering an opening in a panel adjacent to an airbag inflation system comprising: . . . a tether attachment element having a first portion sandwiched between said inner (metal) and outer substrates and second portion exposed for attachment to a tether and at least one tether having a loop at an outer end portion of said tether attachment element and having an inner end portion adapted for fixed attachment to limit the amount of movement of said cover away from the opening deployment of the airbag inflation system”. Col. 9, Ln. 17–25. The tether may comprise a loop and the attachment element may be an elongated metal rod. The attachment element (rod) has a series of U-shapes that extend from between the door inner and outer back to a flexible tether that is looped in its undeployed condition.
U.S. Pat. No. 5,332,257, also to Morton International, discloses a tether having first and second ends, the first end being secured to said module cover (on the B-side), and the second end forming a loop, a retainer rod extending through said loop and a channel enclosing said retainer rod and loop in a fixed position . . . to anchor said tether.
U.S. Pat. No. 5,211,421 to G.M., discloses a tether that is on the A-side of an airbag door, between substrate and foam layer which is fastened to a bracket on the canister.
All of these references use numerous components in an attempt to accomplish their objectives resulting in added material and manufacturing costs. Separate door, chute, tether, fastener and reinforcement materials are combined with a myriad of attachment processes to form an assembly that must be installed in the instrument panel.
It is therefore an object of the invention to provide a tether for an airbag door that has a controlled slack such that the slack tensions, in a controlled and dynamic manner, to retain the door to the instrument panel upon airbag deployment.
More specifically, it is a further object to provide a tether for an airbag door that is secured to the airbag door and wherein the tether shape within the door is defined by engagement to a series of ribs in the door and which tether shape ultimately defines a tether slack that is controllably tensioned upon airbag deployment.
These and other objects, advantages and features of the present invention will become more apparent from the following description and the accompanying drawings.